Problem: In math class, the girl to boy ratio is $5$ to $6$. If there are $30$ boys, how many girls are there?
Explanation: A ratio of $5$ girls to $6$ boys means that there is a group of $5$ girls for every group of $6$ boys. If there are $30$ boys, then there are $5$ groups of $6$ boys each. Because we know the ratio is $5:6$ , there must be $5$ groups of $5$ girls each. There is a total of $25$ girls in math class.